1. Field of the Invention
The present invention relates to a thermostatic fluid flow regulating assembly comprising, by way of the flow-obstructing part, a sleeve whose movements are controlled by a thermostatic element influenced by the temperature of the moving fluid.
2. Brief Description of the Related Art
This kind of thermostatic assembly is used in valves generally employed in cooling circuits used in heat engines of large cylinder capacity, such as those used in lorries and certain motor vehicles, where the fluid flow rates necessary for their operation are higher than those found in heat engines of smaller cylindrical capacity, in which the thermostatic valves are of the shutter type.
The reason for the use of a sleeve is that it generally enables the use of a so-called balanced flow obstructor, that is to say an obstructor where the pressure differential between the two sides of the walls of the sleeve is approximately zero in the direction in which the obstructor is moved by the thermostatic element. This direction corresponds in practice to the axial direction of the sleeve. In contrast to this, in a shutter-type thermostatic valve, the shutter is in a plane perpendicular to the direction in which the shutter is moved by the thermostatic element, which means that the pressure differential between the two sides of the shutter in this direction reaches high values, especially when the fluid flow is interrupted by the shutter. The energy required to lift the shutter off its seat in this condition is often very great, and is greater the higher the flow rate of the fluid to be regulated.
The invention is concerned more particularly with thermostatically controlled sleeves used in combination with a flat bearing seat on an axial end of the sleeve, which is generally in the shape of a flat annular edge. An example of this kind of sleeve is given in EP-A-1 486 843. A fluid flowing radially with respect to the axis of the sleeve can then be regulated by the relative gap between the end of the sleeve and the seat. In particular, when the end of the sleeve is pressed against the seat, this fluid flow is theoretically zero. In practice, however, the sleeve/seat contact allows a certain amount of radial leakage due to the metal/metal nature of this contact. To limit these leaks, it is known practice to overmould the flat seat with rubber. This improves the leaktightness of the contact between the sleeve and the seat. This solution is technically reliable because it is based on technical teaching relating to the overmoulding of the shutters referred to earlier. However, this overmoulding is expensive and often difficult to make compatible, from the technical point of view, with the seat environment, depending in particular on the integration of the thermostatic regulation assembly into a valve housing of a specific geometry. As a result, leaks through the contact between the sleeve and the seat have hitherto very often been tolerated.
U.S. Pat. No. 4,022,377 discloses another example of a thermostatically controlled obstructing sleeve. To improve the regulation of the flow of a fluid between the end of the sleeve and a flat metal seat, a metal insert whose outer face is generally a frustum of a cone is attached to the end of the sleeve and bears against and moves progressively away from the seat, depending on the movements of the sleeve. In this way, fluid admitted between the frustoconical face of the insert and the seat increases in a progressive and controlled manner as the sleeve lifts off the seat. However, because of the rigidity of this insert, which is typically hardened steel, the insert/seat contact when the sleeve is supposed to close the seat leaks in the same way as described above. In the long term, these leaks also tend to increase during burring and/or indentation of the seat by the action of the insert, unless this seat is made of harder, tougher metal, but this increases the cost and does no more than stabilize leakage at a non-zero level.